The invention relates to overcoming three types of problems relates to the use of sewer pipes made of flexible plastic, such as polyvinly chloride, that are placed underground in a trench and covered.
First, it is not rare for such pipes to be forced out of round by improper compaction of the soil in the trench which forces the weight of the soil and other filler material that is piled on top of the pipe when filling the trench to force in the somewhat flexible pipe wall. Government regulations of various jurisdiction vary as to amount of out-of-roundness which can be tolerated, the variation being between about 3% and 10%, but they are substantially universal in requiring that there be very little eccentricity in the pipe.
There have been some devices used to test for out-of-roundness by pulling the device through the string of pipe after backfill and compaction of the material in the trenches have been completed. If the device passes through satisfactorily, the pipe is adequately round. When the pipe is over-deflected, however, the device will not pass through and fails this test. The contractor would be subjected to heavy costs if he were to have to dig up the entire line of pipe and rework or replace the bedding material.
A recently-issued U.S. Pat. No. 4,309,128 describes one apparatus which has as its purpose the solving of this problem of deflection of plastic pipe. This patent, by Richard L. Williams, comprises a cylindrical device, possibly with a tapered nose, which can be pulled through the pipe and which includes an eccentrically mounted weight on a shaft which projects from an air motor. This eccentric weight sets up vibrations inside the cylindrical housing, and the vibrations are transmitted to the housing all around its circumference. These vibrations are said to act to change the soil compaction in such a way as to cause, at least in many instances, the relief of pressure on the top and sides of the pipe, so that the pipe can restore itself to round.
While in that invention the vibrations are in all directions, we have found that it is very important to concentrate or confine the vibrations to substantially the longitudinal vertical plane. This confining produces far better results, both in costs and in relieving the pressure on the top of the pipe. The device of this invention transmits the internal vibration and related forces through the pipe wall, primarily at the top and bottom of the pipe, and the vibration is smallest at the sides of the pipe. These predominantly vertical vibrations compact the filler material beneath the pipe, while at the same time causing a type of compaction above the pipe, forming what is known as a soil arch spaced above the crown of the pipe. This soil arch relieves the pipe from supporting some of the downward pressure of the soil above the soil arch and provides some support itself in that soil. Thus, the present invention is able to re-round over-deflected pipe and to help maintain pipe roundness by providing this "soil arch" above the top of the pipe, as well as by acting on the fill at the sides and bottom of the pipe and so providing the needed support in the soil.
The device of this invention also acts as a gauge to determine the acceptability of the pipe line, including the freedom from substantial deflection, without having to use, in addition, some other gauging device. Only one pass of the device of this invention is needed to accomplish all that is required. Moreover, the device's vibrator need not be operated all the time but only when the device meets resistance to its being pulled through, indicating the approach of over-deflection or actual over-deflection.
The second problem to which this invention relates is that known as "over-belling". The pipe is typically made with a bell and spigot joint. The bell is an end portion which is larger in diameter than the remainder of the pipe; the spigot is simply the other end of the pipe. The spigot of one pipe section is inserted in the bell of a preceding pipe section, which also typically has an annular recess holding a rubber sealing gasket. With clay or concrete or asbestos-cement pipe, the spigot end is rigid, so that "over-belling" is not possible, for the spigot can be inserted only so far. However, plastic pipe, typically polyvinyl chloride, is stress-relievable. The spigot can be forced into the bell beyond the point where the bell ends in a short tapered portion that joins the bell to the cylindrical remainder of the pipe proper; when forced beyond that point, the spigot end deforms under force turning conically inwardly and protruding into the pipe proper. When this happens, the inwardly deformed portion of the spigot reduces the pipe diameter and so obstructs flow. It also prevents the passage of the pipe-roundness testing device or gauge and may result in rejection of the pipeline by the government agency concerned.
We have found that over-belling can be corrected by pulling the vibrating device of this invention toward and against the protruding portion of the spigot of an overbelled joint, the pulling being done at constant force; the tendency of the pipe material to resume its original shape is helped by the vertical vibration (and sometimes by actual contact and pushing) to force the spigot back to its proper position. This is important because, typically, failure of the pipeline to pass the roundness test is due about 40% of the time to over-belling at one or more joint, rather than to other causes. It is nearly as significant a problem as that of deflection due to improper compaction of the trench-filling material.
A third problem results from improper grading or compaction of the bottom of the trench in which the pipe is laid. Uniformity of grade is important in order to insure even flow of liquid through the pipeline. Uneveness of grade causes the line of pipe to go somewhat up and down from section to section. This results in failure of the pipe to meet some other tests that are often used to determine whether sewer pipe has been properly installed, namely, the test of its ability to pass a beam of light from one end of a pipeline to the other and the test of passing a closed-circuit television inspection. In this instance, vibration alone may not solve the problem, but we have found that if, while the device is pulled through the pipe at constant force, and from downstream to upstream, water is flowed downstream around the unit, the vibratory effects causing compaction of the trench bottom can be maximized.
Thus, the invention helps to test for pipe roundness, to restore roundness in deflected pipe, to achieve integrity at the joints, and to correct minor unevenness of grade, so as to assure long pipe life and safety and even flow of liquid through the pipeline when it is in service.
Further, the invention aids in removing debris from the pipe interior, as will be explained later.
Thus, among the objects of the invention are to provide method and apparatus for enabling contractors to comply with sewer roundness and alignment test; to provide plastic pipe sewers which are properly round; to re-round over-deflected pipe; to provide a deflection gauge to determine whether installed pipe is acceptable as to roundness; to act as a cleaning aid for the pipe line ahead of the compactor unit from dirt and other foreign matter; to provide the top, side, and bottom support required for proper action of the sewer pipe over a long period; to solve the problem of relieving over-belled pipelines; and to help to remove sags in the pipeline gradients.
Other objects and advantages of the invention will appear from the following description and drawings of a preferred embodiment of the invention.